Catalytic conversion system



July 11, 1944. D, E, PAYNE 2,353,495

CATALYTIC GONVER'S ION SYSTEM Filed DeC. 3l. 1940 14M, y C

Patented July ll, 1944 cA'rALY'rrc coNvEasIoN SYSTEM Donald E. Payne',Chicago, lll., assigner tovStandard Oil Company, Chicago, Ill., acorporation of Indiana' Application December 31, 1940, Serial No.372,538

Claims. (Cl. 196-52) This invention relates to catalytic conversionsystems and it pertains more particularly to conversion systems of theso-c-alled "fluid" type wherein a solid catalyst is employed forendothermic or exothermic reactions while vsuspended in an upwardlyflowing gaseous or vapor stream. The invention is particularly directedto hydrocarbon conversion ysilzems for the manufacture of high qualitymotor In processes of catalytic cracking, hydrogenation,dehydrogenation, aromatization, reforming,

-isoforming, isomerization, alkylation, desulfurization, polymerization,etc. a hot vaporized hy' drocarbon charging stock `may be contacted witha solid catalystl while that catalyst is suspended in upwardly Aflowingreaction vapor stream. During the reaction the catalyst becomes coatedwith a carbonaceous deposit which impairs its catalytic activity. Thecoated catalyst may be separated from reaction vapors and suspended inanother upwardly fiowing stream containing controlled amountsofoxygengand thus regeneration may be effected by burning off thecarbonaceous ldeposit while the catalyst is lsuspended in hotregeneration gas.

An important consideration in both the reaction and regeneration stepsis the density of the suspended catalyst in the gaseous or vaporsupported medium. It is essential in the reaction step that vaporscontact a suflicient amount of catalyst for a sufficient period of timeto effect the desired reaction. The amount of suspended catalyst in areactor of given size is dependent upon the average density of thecatalyst therein which in turn is critically dependent uponthesuperficial velocity of the supporting gas or vapor in said reactor. Inthe regeneration step it is essential that the coated catalyst besupplied with a sufcient amount of oxygen for eiectingthe necessarycombustion and a suilicient amount of time must be allowed to permit theburningof l the carbonaceous deposit. The amount. of sus# pendedcatalyst in a regenerator of given size is likewise dependent upon theaverage density of the catalyst therein which in turn is criticallydependent upon the superficial velocity of the regeneration gas in theregenerator. The problem in both reactor and regeneratordesign is .toinsure contact of the necessary :amount of catalyst for the necessaryamount of time with the neceslyst in the reactor rapidly increases andthe cata- The' 'catalyst employed may fbe granular,

powdered or pelleted solids of a particle size ranging. from about 10 to400 mesh, preferably about 200 to 4GB mesh and preferably of fairlyuniform size. When such catalyst is introduced at a fairlyconstant vratein the base of a. -vertical reactor wherein there is an upwardly owinggas or vapor stream and the superficial velocity of said stream isvaried it will be found that at high velocities thefcatal'yst movesthrough the reactor at su'bstantially the same velocity as the vaporstreami. e., there; isn-not a great tendency towards settling. At very.low'superflcial vapor velocities through the reactor the catalyst maysettle out of the vapors and assume a quiescent state. Atintermediatevapor velocities the catalyst will be carried'upwardly with thegasstream but there will be a'pronounced tendency toward settling orslipping-i. e. the catalyst will move upwardly in the reactor ata muchlower velocity than the suplyst takes on al boiling appearance in whichbubbles of lgas flow upwardly through a liquid like, dense catalystphase in'a manner similar to the upward ilow of air lthrough a'body ofwater. This settled catalyst takes on the appearance of a new phase, anaer'ated catalyst phase which may have ls. density of 10 to v1Z0-poundsper cubic foot.

This dense phase becomes more pronounced and more clearly deined as thegas velocity, isfurther decreased but if the gas velocity issuicientlydecreased' portions of the catalyst will become quiescent and thoseportions 'of the dense phase sary 'amount of gases or vapors or, inother words,

to obtain the necessary catalyst density and vapor size for effectingthe desired conversion.

will no longer behave as a liquid. In order to y maintain a liquid-likedense phase" condition the uvapor velocity should be at least .2 footper second and preferably about 1 to 2 feet per secbnd. The velocityrequired for such dense phase conditions is dependent of course upon theparticle size and weight of the catalyst, thediameter of the reactor andperhaps to some extent on the viscosity of the gas or vapor streamalthough the viscosity yof this stream is not of as great signifi- Ilcance as has heretofore been assumed.

ging in particle size from about 200 -energy which acts between closelyadjacent particles and holds the powdered catalyst in the dense phasecondition. 'I'he gas whichbubbles through this dense phase sweepscatalyst particles therefrom into the upper gas phase and when suchparticles become dispersed therein they are subject to the laws ofbehavior as individual particles. With the introduction of catalyst intothe dense phase at the same rate at which it is being removed from thetop of the dense phase it is possible to maintain a constant level ofcatalyst in the reactor and to operate in a condition of dynamicequilibrium.

It might be assumed that with such low vapor -velocities there would bea tendency toward classiiication, i. e., for the heavier catalystparticles to settle and escape withdrawal from the upper surfaces. Ithas been found, however,l that with a superficial gas velocity of aboutl/2 to 2 feet per second as much as 40% of 30 to 40 mesh particles canbe added to the powdered catalyst without the occurrence of suchclassication.- After equilibrium has been reached the heavier particlesappear to be swept along in the eddies of relatively dense aeratedcatalyst and to be vdrawn from'the surface of the dense phase at thesame rate as' they are being introduced thereto. A very importantfeature of. the operationv is the uniform temperature which existsthroughout all parts, thereof. Here again' thedense phase apparentlybehaves like a Iliquid in which there is sufficient turbulenceand.convec'' tion currents vto obtain thorough andintimate mixing so lthatalthoughgases mayl be introdense phase' I'cross-sectional reactor area'is system because the pipe still coils, heat exchangers and, in factthe entire system is thus thrown out of balance. Increasing the amountof catalyst introduced into the reactor with the hydrocarbon vapors hasno appreciable effect on the catalyst density in a reactor which isoperating in dense phase condition because said density is primarilydependent upon the vapor velocity, and increasing the amount of catalystintroduced with incoming vapors will merely result in increasing theamount of catalyst discharged from the reactor-i. e. will lessen thecatalyst residence time in a system which is in dense phase equilibrium.

In accordance with my invention I control catalyst density in thereactor by controlling the superficial vapor velocitytherethrough and Icontrol the superficial vapor velocity by varying the effectivecross-sectional area of the reactor while it is on-stream and withoutany interruption or adjustment in any other part vof the system. Thesimplest method of controlling vapor velocity in the reactor istointroduce thereto an. .excess of a. relatively inert gas 'such assteam and to vary the amount of introduced steam to maintain the desiredvapor velocity and catalyst density. .While'steam maybe beneficial forsome.

conversion processes .it is' detrimental to others and it involves acertain added expense. The preferred embodiments of `my invention,therefore,

involve mechanical means for varying the crosslsectionalarea. ofOrl-Stream j `Orne method of mechanically` regulating a to provideareacone .end with means for drawing the other end duced lat. a'temperature `of v950"lfthe yentire n dense.'` phase maybe at atemperature that Y lvery close -to 925 F. when cracking isv being'eiectedin a densephase reactor. Similarly, re# generation temperaturesare uniform throughoutthe entiredense phase and relativelyl cold* gaseswhich are introduced, with the oxygen may maintain any substantiallyuniform regeneration temperature by absorbing the Vexothermicheat'asfastas it is liberated.

ZIn a'commrcial conversion system employing', .the "above described uidtypeup-flow reactor A forsolid catalysts the size `and lcross-sectionalareajof the reactor can be determined for obtaining 4a particular vaporvelocity, catalyst density and catalyst residence time in the reactorfor any given catalyst, lcharging stock, and specificrreaction-conditions.. In commercial operations,

however, the catalyst, charging stock or reaction conditionsmay vary anda reactor designed for one set of conditions may be wholly`unsatisfactory for another set of conditions. This isnparticuiarlytruejwith respect to vapor velocities through the reactor. While thereactor is on-stream it isdesira'ble to have a positive means forcontrolling vapor velocities through the reactor because such vaporvelocities are a chief factor in determining catalyst density in thereactor and hence -the total amountof catalyst which is retained in the`reactor for effecting the desired conversion'.

object of my invention is to provide'a positive around the fixed end toform a tube of variable efl'ective diameter. In another embodiment oftheA invention I provide a tubular reactor with a fixed platefrom thecenter to one side thereof and with another plate rotatable about thecenter and adapted by such rotation to effectively cut out asector lfromthe effective reactor space. By moving one plate toward or away from theother plate the size of this sectional area of the' reactor.' Anothermethod of changing, the veffective cross-sectional reactor area is toprovide a plurality of reactors of different cross-sectional areasconnected for selectiveparallel flow. Various other methods ofregulating effective cross-sectional area may,l of course, be used.

' The yinvention-will bev more clearly understood from thefollowing'detailed description and'from .the accompanying drawing which form-s apart y of thislspeciflcation andin which y i Figure 1 is a flow diagramof my conversion system,

Figure 2 is a horizontal section` of the reactor illustrated in Figure1,

Figure 3 is an isometric view of a modified reactor provided withvariable reactor dead spacel and Figure 4 is a horizontal section of themodification shown in Figure Since the very object of the invention isto pron vide a system of such fiexibility that it may be means for,controlling gas orv vapor velocity through a reactor withoutdisturbing'other parts of the conversion system. Itis highly impracticalfor instance to alter feed rates in 'a V continuous `'employed for awide varietyof processes, it will be obvious that the invention is notlimited to any particularA process. For the purpose of illustration,I.will ,describe` its application vto a process ofgcatalytic `crackingfori the conversion of gas oilinto high quality motor fuel by means ofa- -a reactor while that reactor is which perhaps may 1 sectorV can beeasily and quickly changed for modifying the effective crossassautpowdered catalyst of the silica-alumina type. Such catalyst may beprepared by acid treating bentonite or by depositing magnesio., alumina,or

alumina and zirconia on silica gel. No invention is claimed in anycatalyst per se and it should be understood that the selection of thecatalyst will depend upon the particular process to be carried out inthe apparatus. The cracking catalyst may have a particle size of about200 to 400mesh and may have an apparent bulk density before aeration ofabout .7, i. e. about 40 to 50 pounds per cubic foot. When aerated thecatalyst may have a bulk density ranging from about 20 to 30 pounds percubic foot and a desirable dense phasein a reactor may be about to 20pounds per cubic foot preferably about to l5 pounds per cubic foot;

Gas oil from line III is forced by pump II through coils I2 of pipestill I3 to transfer line Il and thence to reactor I5. Powdered catalystfrom standpipe I6 is introduced into transfer line Il in amountsregulated by star feeder or valve means I1. In this particular case thegas :oil is heated to give a transfer line temperature of about 900 to1050 F., preferably about 975- F. at a transfer line pressure of aboutatmospheric to about 50 pounds, preferably about 15 pounds per squareinch. The catalyst is preferably at about .the same temperature as theheated oil vapors and is introduced into these vapors in a ratio ofabout 5:1 to-1:1, preferably about 3:1 parts by weight catalyst per partbyweight o'f-oil. The catalyst reactor is designed to provide for an oilresidence time in the reactor of 'about 2 to '40 seconds, preferablyabout 10 seconds, with a superilcial vapor velocity therethrough ofabout .3

equilibrium, catalyst particles are-boiledout of the dense phase andlwithdrawn from the s version system.

a rough interface between the dense phase in the lower part of thereactor and a light phase at the top of the reactor. Evidently someforce, such as static electricity or surface energy acts between closelyadjacent catalyst particlesand holds these particles in aerated densephasecon' ditions. From the surface of said dense phase eddies of thereaction vapors may sweep catalyst particles into the lighter upperphase and dis perse them as discrete -particles subject to the laws ofbehavior of individual particles in gas or vapor suspension. Thus, underconditions of reactor at the same rate as they are being introduced intothe reactor with reaction gases.

In order to operate the reactor under optimum dense phase conditions itisfnecessary to critically control vapor velocities in the reactor. Ieffect this control by varying the effective cross-sectional area of thereactor so that an optimum cross-sectional areamay be used for anyparticular catalyst or conversion process or operating conditions and sothat the dense catalyst phase may be held at a constant level in aconversion without unbalancing any other part of the .con-

The reactor illustrated in Figs. 1 and 2 consists of a cylindricalvessel I6 provided with annular top and vbottom plates I6 and 20,.'thelatterV being secured to a conical distributor 2I and the former to 3feet per second, preferably about 1.5 feet per second. The amount ofcatalyst in the reactor will be dependent upon the freshness or activityof the catalyst which, in turn, is dependent upon average catalystresidence time. For catalytic cracking the amount of catalyst in thereactor may he roughly expressed bythe following formula:

T=at-li where T is tons of catalyst in the reactor per hundred barrelsof stock charged to the reactor per hour, a" is a constant ranging from3 to .3,

preferably about 1.2, and t" is catalyst residence v time in minutes.Thus for example, with a 1 minute catalyst residence time a 2,400 barrelper dayplant will require about 3 to .3, preferably 1.2 tons or 2,400pounds of catalyst in the reactor. With an average,.catalyst density inthe reactor of about 12 pounds per cubic foot, the minimum reactorvolume must be about 200 cubic feet.

With a 10 minute catalyst residence' time a 2.400 barrel per day plantmay requirev about 4 tons of catalyst in the reactor. With an averagecatalyst density in the reactor of 12 pounds per cubic, foot the reactorlvolume must be at least about 650 to 700 cubic feet. For obtainingsuperiicial vapor velocity of about 2 feet per second in the reactor thediameter of this reactor must be about 9 or l0 feet. Hence with dueallowance for lower catalyst densities in the upper part of the reactor,such a reactor may be a cylindrical chamber about 9 or 10 feet indiameter and about liquid like phase in thereactor and to pass thereaction vapors through this dense phase much as air would pass upwardlythrough a body of water. 'lat certain critical vapor velocities, usuallyabout .3 to 3 feet per second, there appears to be to a conicalcollector 22. A metal sheet 23 extends between the annular top I9andannular bottom 20 of the reactor this sheet being curved to form aninner cylinder which defines the actual reaction chamber space. One end24 of sheet 23 iswelded or otherwise secured in the chamber in fixedposition. The other end 25 is connected to rods 26 extending throughsuitable packing glands 21 and provides a means for moving the free end26 toward and away from fixed end 24.

The Aamount vof catalyst in the reactor may be determined by differencein pressure inthe top and bottom of the reactorfor exampleby means of asimple manometer. By pushing rods 26 vinwardly the effective reactor'cross-section is increased and the vertical velocity of-up-owing vaporsis correspondingly decreased so that the amount of catalyst in thereactor is increased.' By pulling rods 26 outwardly the effectivecrosssectional area of the reactor is decreased giving a correspondingdecrease in catalyst density in" the reactor. Positive driving means 28may-be employed for'` automatically forcing rods 26 inwardly oroutwardly in accordance with pressure differential across the reactorwhich may be indi-..

cated by a manometer or other suitable means 29. The amount of catalystis; of course, dependent upon reactor volume as well as average catalystdensity in the reactor so that the pressure differential controlleddriving means must be designed to take into account the change inreactor volume as well as pressure differential across the reactor.

The reaction products and suspended catalyst leave the top of thereactor through line 30 and are introduced into cyclone separator 3|from which separated catalyst passesto--the top ofl hopper or strippercolumn 32 provided with baf'f es 33.' The gases from separator 3i may beintroduced yby line 34 to a conventional fractionation system forseparating gasoline, gas and vhydrocarbons heavier than gasoline, thelatter being commonly referred to as cycle o Steam or other inert gas isintroduced through l l instance, reaction chamber 53 may be providedwith a fixed radial plate a, b, c, d, and a movableradial plate m, b, c,n, m. The

line 35 to eiect the stripping and the stripped products. are removedthrough line 38 to line 34. The stripped catalyst then passes tostandpipe or catastat 31 which may be a tower about 50 to 100 feet highand about 3 or 4 feet in diameter. The catalyst in this tower is aeratedby steam or other inert gas introduced through line 38 at such a rateas'to maintain the catalyst in fluent condition, the superficialvelocity of the steam in the tower being about .02 to .2 feet persecond.

Catalyst is withdrawn from the base of the tower through star feeder orslide valve 39, picked up by air introduced through line 40 and passedby line 4| into one or more regenerator chambers 42, 43 or 44. Thediameter of chamber 43 may be twice that of 44 and the diameter of 42may `be twice that of 43. By proper selection of chambers a wide varietyof eiective cross-sectional areas may be obtained and in any particularinstance a selection will be made to provide for a superiicial gasvelocity in the regenerator of about .2 to 2, preferably about 1 to 11/2feet per second. It should be understood, of course, that theregenerator may be a 'chamber of the same type as reactor I and thecross-sectional area may be I controlled in the manner described inconnection therewith. Cooling gases may be added with the air introducedby line 40 or may be introduced directly into the regenerator chambersproviding, of course, that the cross-sectional area of the chambers isproperly selected so that the vapor velocity grill be maintained withinthe critical limits. Temperature control may likewise be effected bycooling a part of the regenerated catalyst and returning the relativelycooled catalyst to chambers undergoing regeneration. In fact, cooling.tubes may be used in the regeneration chamber itself as indicated bycoils 45 for insuring that the regeneration temperature will not exceedabout 1050 F.

Regeneration gases and suspended regenerated catalyst are withdrawnthrough line 46 and line 41 to cyclone separator 48 from whichregeneration gases are vented through line 49 to suitable waste heatboilers or power recovery means. It will be understood that a number ofcyclone separators may be employed in series for eiecting separation orthat other conventional separation means may be employed in placethereof.

From separator 48 the regenerated catalyst falls into hopper 50 which isaerated by an inert gas introduced by line 5I. The catalyst then fallsinto standpipe or catastat I 6 which is aerated by an inert gasintroduced through lirfe 52.

In connection with Figure two different means for regulating effectivecrosssectional reactor area and have indicated that either of thesemeans may be employed for either the -reactor or the regenerator. Itshould be understood that other mechanical means may likewise be usedfor accomplishing this purpose. For (Figures 3 and 4) movable platemayrotate about axis b, c and thus cutout a sector b, a, m (Figure 3) fromthe circular cross-sectionalarea of the reactor. Plate m, b. c, n mayberotated by mechanical means or it may be rotated by fluid pressure, asuitable operating iiuid being introduced or withdrawn y through line54. Thus if the vapor velocity in the reaction chamber becomes too highit may be lowered by moving the movable plate more closely is desired toobtain of reactor space the 75 pOuIldS to the ixed plate and if it asmaller cross-sectional area 1 I have'illustrated for varyingcross-sectional area compris movable plate may be moved away from theiixed plate.

While I have described the regulation of crosssectional reactor area inaccordance with the pressure differences Vin the top and bottom of thereactor it should be understood that other controls may be used. Forinstance, the amount of catalyst discharged fromcyclone separator 3l maybe larger than the amount of catalyst introduced through line I4, thusindicating that vapor velocities in the reactor are too high. Theeffective cross-sectional area of the reactor may then be reducedaccordingly to keep the amount of catalyst discharged from separator 3|equal to the catalyst introduced through line I4. Other methods ofcontrol will be apparent to those skilled in the art from the abovedescription.

I claim:

1. The method of maintaining a critical vapor velocity in an up-iiowreactor of xed external dimensions for maintaining powdered solidcatalyst in dense phase condition in upf-lowing gas or vapor, whichymethod comprises varying the effective cross-sectional area of saidreactor without changing the external dimensions thereof.-

2. In a catalytic conversion system, an u'p-flow reactor of xedexternaldimensions, means for introducing powdered catalyst and asuspending gas at the -base of said reactor, -means for-withdrawingsuspended catalyst and a gas from saidreactor and means for regulatingthe effectivel cross-sectional area of said reactor without changing theexternal dimensions thereof for maintaining a superficial vapor velocitytherein within the approximate range of .3 to 3 feet per second.

3. The apparatus of claim 2 wherein the means an expansible tube.

4. The apparatus of claim 2 wherein the means for varyingcross-sectional area comprises a xed plate in said reactor and a movableplate therein and means for moving said xed plate with respect to saidmovable plate.

5. In a catalytic conversion apparatus an upow reactor, means forintroducing powdered catalyst varying the effective cross-sectional areathereof.

6. In a hydrocarbon conversion system wherein charging stock isvaporized and heated to a conversion temperature and introduced at thebase o per cubic foot in a reaction zone and wherein powdered catalystis continuously introduced into said zone and powdered catalyst andvapors are continuously withdrawn from said zone so that there may be atendency toward an increase or decrease in the amount of catalystin thereaction zone while said zone is on-stream, the method of maintaining asubstantially constant amount of catalyst in the reaction zone whichmethod comprises ascertaining the pressure differential between thebottom and top of said reaction zone, increasing the vertical vaporvelocity in said reaction zone without substantially changing thehydrocarbon vapor charge rate when the pressure differential exceeds apredetermined maximum and decreasingr the verti cal vapor velocity inthe reaction zone without substantially changing `the hydrocarbon vaporcharge rate when the pressure differential falls below a predeterminedminimum.

8. The method of claim 7 wherein the increasing and decreasing of vaporvelocities in the reaction zone is eected by varying the effective whereT is tons of catalyst in the reaction zone per 100 barrels of liquidhydrocarbon stock charged to the reaction zone per hour, "a" is aconstant within the approximate range o! .3 to 3 and "t is catalystresidence time in the reaction zone expressed in minutes.

DONALD E. PAYNE.

